The invention relates to a semi-automatic transmission for motor vehicles, in particular, for commercial vehicles with diesel engines.
Motor vehicles wit diesel engines are normally started so that the ignition key is first switched into a warm-up position. It is then necessary to wait for a certain period of time until the pre-warming process is completed. The ignition key is then turned further so that the electric starter of the engine is switched on. This starting procedure starts up the diesel engine and causes it to then run on at idle speed. In some vehicles, the starter is not actuated by the ignition key, but instead by a separate button.
A semi-automatic transmission is understood herein to be a transmission with a clutch to be actuated by a driver present within the vehicle. The gears are selected or pre-selected by means of an electric transducer, which may be in the form of a stepping switch. There is no mechanical connection between the transducer and the transmission. Instead, the switching signals are transmitted via electric cables ("shift by wire"). The driver receives no direct information from the transducer on whether a gear has currently been selected.
During the start up process described above, it is necessary for the transmission to be in the neutral position or for the clutch pedal to be pushed down, i.e., disengaged from the transmission. If the main clutch is engaged accidentally and a gear is selected during the engine start up procedure, dangers exist that the vehicle may suddenly jump, the motor may stall, or that the transmission may be damaged. The danger especially exists in a vehicle with a semi-automatic, shift by wire, transmission that the driver may not check the clutch and transmission positions before starting the engine.
It is an object of the present invention to avoid the dangerous situations heretofore described.